RE: OT : compress & write to tape - how to ?

Newer versions of tar (GNU) have "z" argument, so it
would work like this: tar zcvf /dev/rmt0 /my/directory
If your tar doesn't support "z" flag, you can do it
like this:
tar cvf - /my/directory |compress|dd of=/dev/rmt0

You can also do it with cpio. If your cpio supports "-C" buffering,
you can play around with dd and speed things up significantly.